It's planned obsolescence through price. Your wife paid >50% of the phone's value just to replace the battery. Many people won't think that's worth it. It could have been a $30 user replaceable battery.
> I don't know that I buy that it's "planned obsolescence".
I'm responding to this. It might be worth it for your wife. But if for a lot of people, paying $100 to revive a 6 year old phone is a bad deal, then it's planned obsolescence
$100 is worth it, but you can get a good discount by going to that one mall kiosk instead of the Apple Store.